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// -*- verilog -*-
//
// USRP - Universal Software Radio Peripheral
//
// Copyright (C) 2003 Matt Ettus
//
//
// NOTE This only works for N=4, max interp rate of 128
// NOTE signal "rate" is EQUAL TO the actual rate (no more -1 BS)
module cic_int_shifter(rate,signal_in,signal_out);
parameter bw = 16;
parameter maxbitgain = 21;
input [7:0] rate;
input wire [bw+maxbitgain-1:0] signal_in;
output reg [bw-1:0] signal_out;
function [4:0] bitgain;
input [7:0] rate;
case(rate)
// Exact Cases
8'd1 : bitgain = 0;
8'd2 : bitgain = 3;
8'd4 : bitgain = 6;
8'd8 : bitgain = 9;
8'd16 : bitgain = 12;
8'd32 : bitgain = 15;
8'd64 : bitgain = 18;
8'd128 : bitgain = 21;
// Nearest without overflow
8'd3 : bitgain = 5;
8'd5 : bitgain = 7;
8'd6 : bitgain = 8;
8'd7 : bitgain = 9;
8'd9,8'd10 : bitgain = 10;
8'd11,8'd12 : bitgain = 11;
8'd13,8'd14,8'd15 : bitgain = 12;
8'd17,8'd18,8'd19,8'd20 : bitgain = 13;
8'd21,8'd22,8'd23,8'd24,8'd25 : bitgain = 14;
8'd26,8'd27,8'd28,8'd29,8'd30,8'd31 : bitgain = 15;
8'd33,8'd34,8'd35,8'd36,8'd37,8'd38,8'd39,8'd40 : bitgain = 16;
8'd41,8'd42,8'd43,8'd44,8'd45,8'd46,8'd47,8'd48,8'd49,8'd50 : bitgain = 17;
8'd51,8'd52,8'd53,8'd54,8'd55,8'd56,8'd57,8'd58,8'd59,8'd60,8'd61,8'd62,8'd63 : bitgain = 18;
8'd65,8'd66,8'd67,8'd68,8'd69,8'd70,8'd71,8'd72,8'd73,8'd74,8'd75,8'd76,8'd77,8'd78,8'd79,8'd80 : bitgain = 19;
8'd81,8'd82,8'd83,8'd84,8'd85,8'd86,8'd87,8'd88,8'd89,8'd90,8'd91,8'd92,8'd93,8'd94,8'd95,8'd96,8'd97,8'd98,8'd99,8'd100,8'd101 : bitgain = 20;
default : bitgain = 21;
endcase // case(rate)
endfunction // bitgain
wire [4:0] shift = bitgain(rate);
// We should be able to do this, but can't ....
// assign signal_out = signal_in[shift+bw-1:shift];
always @*
case(shift)
5'd0 : signal_out = signal_in[0+bw-1:0];
5'd3 : signal_out = signal_in[3+bw-1:3];
5'd6 : signal_out = signal_in[6+bw-1:6];
5'd9 : signal_out = signal_in[9+bw-1:9];
5'd12 : signal_out = signal_in[12+bw-1:12];
5'd15 : signal_out = signal_in[15+bw-1:15];
5'd18 : signal_out = signal_in[18+bw-1:18];
5'd21 : signal_out = signal_in[21+bw-1:21];
5'd5 : signal_out = signal_in[5+bw-1:5];
5'd7 : signal_out = signal_in[7+bw-1:7];
5'd8 : signal_out = signal_in[8+bw-1:8];
5'd10 : signal_out = signal_in[10+bw-1:10];
5'd11 : signal_out = signal_in[11+bw-1:11];
5'd13 : signal_out = signal_in[13+bw-1:13];
5'd14 : signal_out = signal_in[14+bw-1:14];
5'd16 : signal_out = signal_in[16+bw-1:16];
5'd17 : signal_out = signal_in[17+bw-1:17];
5'd19 : signal_out = signal_in[19+bw-1:19];
5'd20 : signal_out = signal_in[20+bw-1:20];
default : signal_out = signal_in[21+bw-1:21];
endcase // case(shift)
endmodule // cic_int_shifter
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